docs: def unpack_value(format_string, stream):
      """Helper function to unpack struct data from a stream and update the signature verifier.
  
      :param str format_string: Struct format string
      :param stream: Source data stream
      :type stream: io.BytesIO
      :returns: Unpacked values
      :rtype: tuple
      """
      message_bytes = stream.read(struct.calcsize(format_string))
      return struct.unpack(format_string, message_bytes)